Metal-working.



- invention is of general application to the- STATESFPA-TENTOFFIGE' WILLIS R. WHITNEY, OF SCHENECTADY, NEW YORK, ASSIGNOB [0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

Patented Nov. 14, 1911.

METAL-WORKING.

1 008,762 Specification of Letters I Patent.

Ho Drawing.

Application filed March 28, 1910. Serial No. 551,156.

chromium group, such as tungsten or molybdenum, are pointed expeditiously, leaving a clean surface free from pits or scars. My

chemical removal, or corrosion, of these metalsand can be used for other purposes,

as for example, to clean dies accidentally plugged.

If it is desired to point a rod consisting of a metal 'of the chromium group, as for example, tungsten, the rod is dipped into a 1 fused bath consisting of an oxidizing'salt,

preferably a bath consisting 3 of a fused nitrite, such as potassium or sodium nitrite; The nitrite need not be pure. I find the commercial salt which ordinarily contains small amounts of impurities, such as chlorids, answers very well for the'purpose. In some cases it is advantageous to heat the ends of the rod or filament before dipping into the fused bath, but it is usually sufficient to simply dip the rod or wire m-to the fused bath. In fact, the heat generated by the chemical action of the nitrite on the wire heats the wire to redness. If it is desired to clean a steel die plugged with tungsten,

, for example, the die is simply dipped into the fused nitrite and the tungsten is thereby dissolved out without any appreciable corrosion of the steel taking place. Other oxidizing baths, for example, the nitrate of sodium, or of potassium, can be used, but, in this case, a diluent, such as the chlorid of sodium 2. The process of chemicall removing all a or a part of a body of metal 0 the chromium roup, which consists in bringing the metal into contact with a fused bath containing a nitrite. V

3. The rocess of pointing a tungsten rod or wire w ich consists in dipping an end of said rod or wire into a fused nitrite.

' 4. The process of dissolving, or corroding, a solid body of tungsten which consists in bringing it into contact with a fused nitrite.

5. In the process of drawing tungsten, the steip which consists in pointing the tungsten ro or wire, by dipping it into fused potassium nitrite.

6. The process of dissolving, or corroding, a body of tungsten which consists in bringing it into contact with a commercial salt of nitrous acid maintained at an elevated temperature.

7. The process of corroding a body of metal of the chromium group which consists in acting'upon it with a fused oxidizing 

